The present invention relates to an air-fuel ratio controller having a feedback system in which the air-fuel ratio of the mixture formed in the carburetor is controlled in accordance with a signal derived from an exhaust gas sensor and, more particularly, to an improvement in an actuator for use in the feedback system and adapted for effecting the control of the air-fuel ratio.
There have been proposed and actually used various types of air-fuel ratio controllers of the kind described. In a typical conventional air-fuel ratio controller, as will be explained later in more detail, a passage communicating with the air bleed of the main system and a passage communicating with the air bleed of the slow system of the carburetor are opened in a common valve seat which is flat and adapted to make a surface contact with a cooperating flat valve. Therefore, if the valve is mounted at a slight inclination or if the valve seat is not sufficiently finished, the passages leading to respective air bleeds often communicate with each other, even when the valve is seated on the valve seat. In such a case, since the vacuum in the slow system is greater than the vacuum established in the main system, the fuel is inconveniently induced from the main system into the slow system.